A cruise ship heading for New York this month struck and killed a whale and dragged it into the Hudson River, part of a higher-than-usual rate of strikes along the Eastern Seaboard for this time of year, a federal agency said.

In a similar case, a sei whale was found dead and attached to a container ship that was docking near Philadelphia, NOAA said.

The whales may be following food sources closer to shore, NOAA said. An increased food supply has recently been cited for a large increase in the number of humpback whales off Massachusetts.

The agency issued a reminder to mariners of measures already in place to protect whales, including speed limits and distances.

“Nobody wants to hit a whale,” said Marjorie Mooney-Seus, a spokeswoman. “So we want people to have a greater awareness that they’re out there now.”

The rotting blue whale carcass is seen on the shore of Trout River in Canada on April 27.APThe usual rate of whale strikes by ships is about one every few weeks, she said, compared with the three in the past few weeks.

NOAA said it counted 28 whale strikes in Northeastern waters between 2006 and 2010. Worldwide, a National Marine Fisheries Service survey covering 1975 through 2002 found 292 records of confirmed or possible ship strikes to large whales.

Rob DiGiovanni, who heads a marine mammal rescue group on Long Island, said he’s seeing “more evidence of ship strikes and that’s definitely a concern.” In the past, his Riverhead Foundation for Marine Research and Preservation would go a couple of years without seeing a large whale that had been hit by a ship.

“Now we get a couple a year,” he said.

NYPD Harbor Patrol tows the whale to the New Jersey side of the harbor.Edwin LopezThe New York cruise ship incident was discovered May 4, the Philadelphia case on May 7, Mooney-Seus said. She did not have details about the third recent strike except that it involved a fin whale; NOAA is investigating.